1. Field of the Invention
This invention relates to a power divider/combiner and more particularly to a power divider/combiner that has bandpass filters connected into a circuit thereof.
2. Description of the Prior Art
Power dividers/combiners are known. A power divider, often also referred to as a power splitter, and a combiner have an identical structure. A power divider can be used as a power combiner simply by reversing the input and outputs. For example, when a power divider has one input and two outputs, it can be used as a power combiner having two inputs and one output, the flow of current through the device simply being reversed.
Planar microwave circuits have utilized distributed transmission line structures for the design of active and compassive components (i.e. microstripline and co-planar waveguide structures are the most common). Lumped elements have been used below frequencies of 1,000 MHz.
A paper by Seymour B. Cohn, entitled "A Class of Broad Band Three-Port TEM-Mode Hybrids" was published in IEEE Transactions on Microwave Theory and Techniques, Volume MTT-16, No. 2, in February of 1968. The Cohn paper describes a three-port hybrid that can be used as both a power divider and power combiner. When used as a divider, power entering the input port is said to split equally and with zero phase difference between the output ports. The output ports are said to be highly isolated and the general form of circuit is a T junction followed by a multiplicity of cascaded pairs of TEM line lengths and interconnecting resistors. For bandwidths up to about 1.4:1 the performance is stated to be quite good but at the edges of a 2:1 band, the isolation is only 14.7 dB and the input port VSWR is stated to be 1.42. In a paper by Li, et al. entitled "CAD/CAE Design of an Improved, Wideband Wilkinson Power Divider" in Microwave Journal in November of 1984, it is stated that the Wilkinson power divider does not satisfactorily perform in broad band tests done from 2 to 18 GHz. The suggested improvement is to replace linear sections of the Wilkinson divider with circular sections.
It is known to have interdigital capacitors in lumped element microwave circuits (See "Interdigital Capacitors and Their Application to Lumped-Element Microwave Integrated Circuits", by Gary D Alley IEEE Transactions on Microwave Theory and Techniques, Volume MTT-18, No. 12, Dec. 1970). The difficulty in obtaining acceptable wideband isolation at bandwidths greater than 1.4:1 can be at least partially overcome by increasing the number of sections in the power divider. However, due to size and mass limitations, particularly in satellite applications, this approach is rendered impractical.